Ouch!
What you can do is hand express off just enough milk to relieve the pressure - you don't want to express/pump too much, as that will stimulate more milk production. But if you just relieve the pressure a bit, that will help keep you comfortable while your body stops making milk. Watch out for plugs! You might try warm compresses and ibuprofen to help, and if a plug starts, you can take lecithin to keep the milk from backing up too badly. More info here:
http://www.kellymom.com/bf/weaning/weaning_mom.html
HTH!

http://www.kellymom.com/bf/weaning/weaning_mom.html
HTH!